1. Field of the Invention
The present invention relates to derailleurs for cycles and more particularly to the mounting thereof on the frame.
2. Description of the Prior Art
It is known that a derailleur is usually carried by a support plate which is secured to the rear frame lug of the bicycle. The assembly comprising the derailleur and its support plate is mounted in two stages. First of all, this assembly is placed in position on the frame lug and secured to the latter by a screw and nut device. Thereafter, when mounting the wheel hub, the support plate is secured to the frame lug at the same time as the hub.
The fact of first of all securing the support plate to the frame lug by means of a screw and nut device has many drawbacks.
Firstly, there must be employed a special nut which has two shoulders which ensure the guiding in the slot or slideway of the frame lug and two wings or ears which bear against the rear face of this frame lug. This nut is consequently relatively expensive since its production implies a turning operation.
Another drawback resides in the fact that, upon the assembly of the derailleur and its support plate, this screw and the nut, which will subsequently secure the plate to the frame lug, must be mounted on the plate. This consequently implies a first slight tightening of the nut and the screw followed by an untightening in order to permit the mounting of the plate on the frame lug, and a further tightening for fixing the plate in position. Note that this second tightening operation is delicate since it requires the use of two spanners and the support plate must be at the same time correctly positioned with respect to the frame lug. There is also a risk, in the course of the various derailleur handling operations, of the screw and nut becoming untightened and coming away from the support plate.